The present invention relates to swirlers for the fuel injectors of combustors of gas turbine engines and in particular to swirlers for the fuel injectors of lean burn combustors of a gas turbine engine.
Fuel injection systems deliver fuel to the combustion chamber of an engine, where the fuel is thoroughly mixed with air before combustion. One form of fuel injection system well-known in the art is a fuel spray nozzle. Fuel spray nozzles atomise the fuel to ensure its rapid evaporation and burning when mixed with air.
An airblast atomiser nozzle is a type of fuel spray nozzle in which fuel delivered to the combustion chamber by a fuel injector is aerated by swirlers to ensure rapid mixing of fuel and air, and to create a finely atomised fuel spray. The swirlers impart a swirling motion to air entering the combustion chamber, so as to create a high level of shear in the fuel flow.
Typically, an airblast atomiser nozzle will have a number of swirlers. An annular fuel passage between a pair of swirlers feeds fuel onto a pre-filming lip. Thus a sheet of fuel is formed that breaks down into ligaments. These ligaments are then broken up into droplets within the shear layers of the surrounding highly swirling air, to form the fuel spray stream that is emitted from the fuel injection system.
One type of fuel injection system that may have airblast atomiser nozzles is a lean burn fuel injector. A typical lean burn injector 100 is shown in FIG. 2 and is in general circularly symmetrical about a central axis (or swirl axis) 101. A central pilot airblast fuel injector 102 is positioned on this axis 101. Inner and outer pilot swirlers 104,106 are located radially inwards and radially outwards of the pilot fuel injector 102 respectively. The pilot fuel outlet 108 is positioned downstream of the inner and outer pilot swirlers 104,106 and between the inner and outer pilot airflows. These airflows promote atomisation of the fuel injected into the combustion chamber at the pilot fuel injection point 108.
An annular mains airblast fuel injector 110 is located radially outwards of the pilot fuel injector 102. Inner and outer mains swirlers 112,114 are located radially inwards and radially outwards of the mains fuel injector 110 respectively, and provide a swirling airflow for atomisation of the fuel injected at the mains fuel outlet 116.
When the gas turbine engine is operating at low power, only the pilot fuel injector is activated. As engine power is increased, some of the mains fuel supplies are activated, until at high power the mains and pilot fuel injectors are both fully active.
The configuration of the inner and outer swirlers of an airblast fuel injector plays a role in controlling the efficient mixing of air and fuel and so influences the smoke emissions and NOx emissions from the burning fuel.